1. Field of Invention
The invention relates to an ink jet recording apparatus, and, more particularly, to an ink jet recording apparatus that includes a device for circulating ink between a print head and an ink tank to remove air bubbles in the ink circulation channel.
2. Description of Related Art
In a known ink jet recording apparatus that ejects ink onto a recording medium based on input signals, ink is supplied from an ink tank to a plurality of ink ejection channels of a print head, through an ink channel. Actuators, such as heating elements and piezoelectric elements, of the print head are selectively driven to eject ink from the tips of the ink ejection channels (nozzles).
For example, U.S. Pat. No. 4,380,770 and Japanese Laid-Open Patent Publication No. 2000-103084 disclose ink jet print heads that execute a circulation purge operation by circulating ink through the ink circulation channel to remove air bubbles in the ink circulation channel. More specifically, the ink circulation channel is provided between a manifold or a reservoir connected to a print head and an ink tank. The ink circulation channel includes a first ink channel for guiding ink from the ink tank to the manifold, and a second ink channel for returning or collecting ink from the manifold to the ink tank. Each of the first and the second ink channels is connected to the manifold and the ink tank. An ink circulation pump is provided in the second ink channel. Using the ink circulation pump, ink is circulated through the ink circulation channel from the ink tank to the manifold through the first ink channel, and from the manifold to the ink tank through the second ink channel. Air bubbles in the ink circulation channel are forced into the ink tank by the ink circulation purge operation, along with the circulating ink. The air bubbles are released from the ink tank to the atmosphere.
U.S. Pat. No. 4,380,770 and Japanese Laid-Open Patent Publication No. 2000-103084 also disclose execution of a suction purge operation after the circulation purge operation. In the suction purge operation, the second ink channel is closed and a nozzle surface of the print head is covered with a suction cap. By driving a suction pump, air bubbles are removed from the ink ejection channels of the print head, together with the ink in the ink ejection channels.
Print heads have been downsized as technology in the field has advanced in recent years. Accordingly, the size (volume) of the manifold and the ink storage capacity of the manifold have been reduced. If the air bubbles enter a manifold of smaller size, for example, when ink is directly supplied to the manifold after an ink tank is replaced, the ratio of air bubbles to ink in the manifold becomes higher. Further, air enters the manifold through a flexible tube of, for example, the first ink channel, because the flexible tube inevitably has a characteristic that air permeates the flexible tube. Air entering through the flexible tube is dissolved in the ink in the tube and develops into air bubbles with the passage of time. The air bubbles eventually enter the manifold. The manifold is disposed above the ink ejection channels of the print head, so that the air bubbles in the manifold are likely to be pulled into the ink ejection channels of the print head. Entry of the air bubbles into the ink ejection channels causes ink ejection failures.
To prevent the above-described drawbacks, it is contemplated that a buffer tank with larger capacity is provided at a position higher than the manifold and between the manifold and the first and second ink channels. The first and second ink channels are provided between the buffer tank and the ink tank. An ink circulation pump is provided in the second ink channel. The ink circulation purge is performed using the ink circulation pump by circulating ink between the ink tank and the buffer tank through the first and second ink channels.
However, when a ceiling of the buffer tank is substantially horizontal and an outlet to the second ink channel is formed at a portion of the horizontal ceiling of the buffer tank, air bubbles do not readily or smoothly move toward the outlet even if the air bubbles to be removed from the ink in the buffer tank are moved upward to the ceiling. Accordingly, the air bubbles are incompletely removed.
Ink jet recording apparatuses are generally placed on a substantially horizontal surface, such as a table or a shelf board. However, if an ink jet recording apparatus is placed at an angle or slightly inclined, such that the ceiling of the buffer tank on the side of the outlet is lowered, the air bubbles collect in the uppermost portion of the buffer tank, so that the air bubbles in the buffer tank cannot be removed.
Accordingly, one aspect of the invention is to provide an ink jet recording apparatus that includes a device for removing air bubbles in an ink channel and separating air bubbles from the ink using simple structures.
According to one aspect of the invention, an ink jet recording apparatus may include a print head that has a plurality of ink ejection channels, an ink tank that stores ink, a buffer tank that has an inlet and an outlet and stores the ink supplied from the ink tank, a first ink channel that supplies the ink from the ink tank to the buffer tank through the inlet, a second ink channel that collects the ink from the buffer tank to the ink tank through the outlet, and a pump that is activated to remove air bubbles by circulating the ink between the ink tank, the first ink channel, the buffer tank, and the second ink channel, and wherein the outlet is disposed higher than the inlet at a ceiling of the buffer tank.